This invention relates to an improved power supply for a television receiver.
Often it is desirable to derive operating voltages for a television receiver from alternating current produced in the horizontal deflection system. Such current may be obtained from secondary windings of a transformer which forms the coupling between a switched mode power supply, operating at the horizontal scanning frequency, or some other frequency and the deflection system, such as described in copending United States application Ser. No. 607,512, entitled "Synchronized And Regulated Power Supply," or from a winding of the horizontal output transformer. Such arrangements eliminate the need for a separate mains transformer and the relatively high frequency alternating current may be smoothed by smaller capacitors than otherwise required for the mains current frequency.
Under some circumstances the variable loading of the audio circuit on the horizontal deflection system causes the width of the picture to be varied at the audio rate. Similarly if the vertical deflection system operating voltage is derived from the horizontal system the picture height as well may be modulated at the audio rate. Of the known techniques for reducing the effects of audio modulation such as the use of a separate mains transformer for the audio power supply, use of a conventional shunt stabilizer coupled between the secondary winding and the audio circuit, and, the use of very careful circuit design with highly sophisticated smoothing networks, the first is very expensive, the second calls for a high power consumption and the third requires complex design and is not always possible.
In accordance with a preferred embodiment of the invention, a transformer includes a core providing a main flux path, a primary winding and at least first and second windings. The primary winding is coupled to a source of alternating current in a power supply and deflection system and is wound around the core for establishing flux therein. The first winding is closely wound around the core to have a voltage induced therein by the main flux of the core and is coupled to provide operating voltage to a first load. The second winding is loosely wound about the core without encircling any leg thereof so as to have a voltage induced therein primarily by the leakage flux of the transformer, the second winding being coupled to provide operating voltage for a second load such that variations in the second load current have substantially no effect on the deflection system and first load voltages.